The present invention relates to a laminated sintered metal structure, a method for the manufacture thereof and, more particularly, a medical application therefor.
Many applications require metal elements, e.g. tubular metal elements, which are porous and yet possess sufficient strength.
Use of a porous flat metal fibre web, sintered or not, is known in various fields of application, e.g. for burners and filters. However, a structure obtained through the winding up of such fibre web has insufficient strength for many applications. In addition, it is disadvantageous for many applications that the core of the tubular element is not sealed off from the casing or, in other words, that the tube wall is radially porous.
In U.S. Pat. No. 3,505,038 it is disclosed how a tubular filter element can be manufactured by combining a metal fibre web, sintered or not, with a metal wire net.
It is an object of the present invention to provide a simple sintered metal structure which has a porous outer wall yet sufficient mechanical strength, and whereby the total wall of the structure is impermeable in the radial direction for the fluids contained in the tube. It is another object of the present invention to provide a method for the manufacture of such a metal structure.
According to a first aspect of the present invention, there is provided a laminated or layered metal structure including a radially outer component and a radially inner component concentrically interconnected with each other. The radially outer component has a porosity of at least 80% and may be composed of sintered metal fibres. The radially inner component is a radially impermeable element, which gives strength to the metal structure and may be a metal foil or a thin metal tube or pipe. The sintered metal fibres give the required porosity to the structure whereas the metal foil gives the impermeability and the required strength to the structure.
Both components can be made of any metal or metal alloy whatever. Examples are steel, stainless steel or titanium.
The radially outer component contains metal fibres that can be made by abrading the upper edge of a rolled metal foil, so-called Bekinit fibres, as described in U.S. Pat. No. 4,930,199, or using the bundled drawing technique, as described, e.g., in the patent U.S. Pat. No. 3,379,000. The metal fibres have an equivalent diameter ranging between 2 xcexcm and 150 xcexcm, preferably ranging between 40 xcexcm and 80 xcexcm. The equivalent diameter of a fibre is the diameter of an imaginary round fibre having the same cross-section as that of the real fibre concerned.
The metal fibres are then processed to form a contiguous porous fibre layer, for example in the form of a nonwoven web, a knitted, woven or wound fabric or mesh, or in the form of helicoidally and diagonally cross-wound metal fibre filaments.
For specific applications, the metal structure is a tubular structure and can be provided with longitudinal anchoring or reinforcing ribs along the outer wall, which, among other things, would enhance its mechanical strength. Transverse anchoring or reinforcing ribs can also be provided around the outside of the tubular structure. Both the longitudinal ribs and the transversal ribs can be of a sintered metal fibre construction, e.g. a sintered steel, stainless steel or titanium fibre construction.
The coated tubular structure according to the present invention can be made of completely bio-inert titanium, thus making the structure exceptionally useful for medical applications. An example of this will be discussed hereunder.
In a preferable embodiment of the present invention, the metal structure has the form of a frustum of a cone. As will be explained hereinafter, such a form allows to have better sintered bonds between the individual steel fibres or steel filaments.
According to a second aspect of the present invention, there is provided a method of manufacturing a metal structure according to the first aspect of the present invention. For an embodiment of the metal structure where the radially outer component is a sintered nonwoven web, the method of manufacturing comprises the following steps:
(a) wrapping a metal foil around a core;
(b) wrapping a metal web around the metal foil;
(c) clamping the foil-web structure obtained in (b) in a mould;
d) sintering the clamped structure in a furnace.
For an embodiment with two or more longitudinal ribs on the outer surface, the method of manufacturing comprises the following steps:
(a) wrapping a metal foil around a core;
(b) wrapping a metal web around the metal foil;
(c) clamping the foil-web structure obtained in (b) in a mould with two or more longitudinal slits down the inner wall;
(d) sintering the clamped structure in a furnace.
According to the third aspect of the present invention, there is provided a use of a metal structure according to the first aspect of the invention as anchorage for foreign bodies implanted in an organic tissue. More particularly, there is provided the use of such a metal structure in continuous ambulant peritoneal dialysis (CAPD) treatment for anchoring a catheter in a human body.
According to a fourth aspect of the present invention, there is provided the use of a metal structure according to the first aspect of the present invention as a heat exchanger.